The present invention relates to a dental light hardening apparatus which is suitable not only for the complete hardening of photo polymerizable dental material but is also suitable for whitening of teeth as well as for deployment as a diagnostic apparatus for cavities. Other therapy possibilities, which are not herein mentioned, can be realized with the dental light hardening apparatus of the present invention. In the following description, the dental light hardening apparatus of the present invention is described including a configuration thereof as a dental restoration piece hardening apparatus.
Light devices have been deployed, among other applications, in dental applications in which a light polymerizable plastic is hardened by irradiation with light. In order to achieve a high light density, energy rich light sources are typically deployed such as halogen glow lamps, xenon photoflash, or even high-tension discharge lamps. The high-tension discharge lamps have, in fact, an especially high light intensity and, thereby, a correspondingly high light density. However, the operational tension reaches at least 3.5 kV and a corresponding activation device is required so that such lamps are not suitable for deployment in the dental practice-at least, insofar as hand operable devices are concerned.
Numerous attempts have been undertaken to improve the light density of the known light apparatus in order to achieve a complete hardening of the deeper lying layers in a rapid manner. A long-time known, conventional light hardening apparatus with a light intensity of, for example, 50 mW/cm2 produces, in fact, by a correspondingly longer light irradiation, a good over surface hardening of the plastic or artificial piece that is to be polymerized. However, deeper lying layers are not at all hardened or, at most, only incompletely hardened. There arises a hardness gradient which leads to the result that the deeper lying, middle regions remain somewhat soft or that these regions are hardened completely at a time later than the complete hardening of the over surface areas.
The known light hardening apparatus lead to restoration results that are compromised by, or suffer from, in part, edge spalling problems. The known light hardenable plastics shrink slightly during the hardening process. With the known light hardening apparatus, a complete hardening initially occurs first in the over/outer regions of the restoration piece. The thereafter following complete hardening of the deeper lying, central regions leads to contractions and, thus, to edge spalling formation.
It is further known to deploy light hardening apparatus that work with semi-conductor light beam sources such as LEDs. For example, DE-GM 295 11 927 discloses a light-hardening device which uses a light diode which emits light in the blue spectral region which is supplied from a battery or an accumulator.
It has, additionally, already been proposed to deploy a plurality of LEDs for the energy supply of the light guiding conduit. In this manner, the light output of the light-hardening device is improved. Independent of whether the LEDs are configured as module—that is, in a common plastic housing—or as individual LEDs—that is, each respectively disposed in an individual plastic housing the light output of such arrangements is limited. The plastic surroundings do not effect an electrical insulation of the LEDs but, instead, block the transfer or giving off of heat by the LEDs, so that it is necessary, even with a cooling of the plastic housing from the exterior, that a predetermined density of the light emitting chips not be exceeded.
It has further been proposed to use a light emitting diode as a semi-conductor light source, which emits light in the visible or ultraviolet range. However, there are disadvantages associated with this approach. Investigations have shown that color changes occur precisely in connection with light or non-dark materials. On the other hand, such conventional systems do not permit the use of white photo initiators.
At the same time, the tendency of the dental restoration piece to suffer from edge spalling formation remains unabated in connection with the conventional systems.